1. Field of the Invention
The invention concerns wireless local area networks and the communications between the devices forming such a network. More specifically, the present invention relates to a communication scheme which allows devices within the wireless local area network to announce their service and/or discover services provided by other devices.
2. Description of the Related Art
Computer terminal and peripherals have become dramatically smaller and more portable. Personal computers and peripherals are small enough to sit on the desk at work. Smaller still are lap top computers and notebook computers. There are computer terminals which are small enough to be mounted in a vehicle such as a delivery truck. Still smaller are the hand-held terminals typically used for their portability features where the user can carry the terminal in one hand and operate it with the other. A physical connection of the above devices by means of cables or fibers may have drawbacks, such as configuration constraints which limit the number of peripherals that can be attached or cumbersome reconfiguration of hardware devices. Note that there are some cable or fiber-based communication systems where the limited number of ports on the computer may not limit the number of peripherals. Ethernet is one example of a communications system where the cable is used as a shared medium (other examples are token ring, FDDI (Fiber Distribution Data Interface), and DQDB (Distributed Queue Dual Bus)).
The smaller the devices get, the more important it becomes to replace fixed physical connections with wireless ad-hoc connections (e.g. body networks, radio frequency connections, or infrared connections), since physically connecting the computer terminals, peripherals, and other devices by means of cables or fibers severely reduces the efficiency gained by making the units smaller. Ad-hoc connections are required where devices are moved within an area, enter an area, or exit an area. The term xe2x80x9cad-hocxe2x80x9d refers to the need for frequent network reorganization.
Local area communication is rapidly evolving into what can be called personal local area networks, which are networks for communication between local peers or subsystems. These networks will herein be referred to as local networks. Wireless communication is of particular importance in such local networks. There are wireless communication approaches that have been developed and designed with an eye on the communication between peers or subsystems of such local networks.
A typical example of a local network is the personal area network (PAN) which grew out of work between two research groups at the Massachusetts Institute of Technology""s (MIT) Media Laboratory. The PAN technology uses a tiny electrical current to transmit a user""s identification and other information from one person to another, or even to a variety of everyday objects such as cars, public telephones, and automated teller machines (ATMs). Information is transferred via microprocessors that are placed in PAN transmitters and receivers the size of a thick credit card. The digital data is then sent or received via a tiny external electric field. The small signal is conducted by the body""s natural salinity and carries the information, unnoticed, through the body. The natural salinity of the human body makes a person an excellent conductor of electrical current. The PAN technology takes advantage of this conductivity. The low frequency and power of the signal ensures that the information, which is coded to the individual, does not travel beyond the body and can only be received by something, or someone, in contact with the body. The speed at which the information is currently transmitted is equivalent to a 2400-baud modem. Theoretically, 400,000 bits per second could be communications using this method. The PAN is a typical example of an ad-hoc body network which does not require any fixed cabling or the like.
The PAN technology has potential applications in business, medical, retail, and even in personal arenas. Business associates could, for example, exchange electronic business cards with a handshake, corporate security devices could automatically log users on and off computer systems, and subway commuters could pay for a ride by walking through a turnstile. PAN technology could also enable people to carry digital versions of their medical records for instant access by emergency medical technicians; calling card numbers could automatically be sent from a wallet to a payphone; and ATMs and automobiles would be able to immediately distinguish their owners as they approach. Another application lies with securities traders, needing the ability to quickly and reliably log on and off while on the trading floor, for entering purchases and sales. Even household devices, such as CD players, televisions and toasters, could identify and adapt to individual preferences and tastes using PAN technology. The PAN networks are usually point to point where the human body serves as a broadcast communications medium.
GTE Corporation has developed a short-range radio-frequency (RF) technique which is aimed at giving mobile devices such as cellular phones, pagers, and handheld personal computers (PCs) a way to interact with one another. GTE""s technique is tentatively named Body LAN (local area network). The original development of Body LAN was via a wired vest with which various devices were connected (hence the name Body LAN). This graduated to an RF connection.
Xerox Corporation has developed a handheld computing device called PARC TAB. The PARC TAB is portable yet connected to the user""s office workstation through base stations which have known locations. The PARC TAB base stations are placed around a building, and wired into a fixed wired network. The PARC TAB system uses a preset building layout and identifiers of the various base stations to determine its location based on the strongest base station signal. A PARC TAB portable device has a wireless interface to the base stations. The PAC TAB system assumes that the PARC TAB portable device is always connected to the network infrastructure. The location of each portable PARC TAB device is always known to the system software. The base stations establish regions and are connected to power supplies. PARC TAB communication systems have a star topology.
In an attempt to standardize data communication between disparate PC devices several companies, including Ericsson, IBM, Intel, Nokia, and Toshiba established a consortium to create a single synchronization protocol (code-named Bluetooth) to address problems arising from the proliferation of various mobile devices. There are many other adaptor companies. The proposed solutions would automatically synchronize mobile devices when end-users enter their offices. Enabling seamless voice and data transmissions via wireless, short-ranged ratio, the Bluetooth technology will allow users to connect to a wide range of devices easily and quickly, without the need for cables, expanding communications capabilities for mobile computers, mobile phones and other mobile devices. The Bluetooth operating environment is not yet fully defined, but there are expected to be similarities with the IrDA (Infrared Data Association) specification and the Advanced Infrared (ALr) specification. Further developments in Bluetooth may stem from the IEEE standard 802.11 and/or HIPERLAN, as promulgated by the European Telecommunications Standards Institute (ETSI).
Bluetooth radio technology provides a mechanism to form small private ad-hoc groupings of connected devices away from fixed network infrastructures. Bluetooth makes a distinction between a master unit, which is a device whose clock and hopping sequence are used to synchronize all other devices, and slave units in the same network segment. In other words, the Bluetooth approach is centralized. A query-based discovery scheme is used for finding Bluetooth devices with an unknown address. Queries are also centralized at a registry server. A drawback of such a centralized approach is the presence of a centralized point of failure. Another disadvantage of such a system includes the overhead required, as compared to a distributed scheme. The main problem of a centralized system is in locating a single registry server, and what to do if it disappears. If two random devices encounter each other they must first recognize each other""s presence, then decide which is the registry server, and then go about their business of communicating. This continual selection and re-selection of a leader causes the increased overhead. The alternative is to expect users to carry one device as the leader at all times. This, however, is not always a practical option. Further details can be found in Haartsen, Allen, Inouye, Joeressen, and Naghshineh, xe2x80x9cBluetooth: Vision, Goals, and Architecturexe2x80x9d in the Mobile Computing and Communications review, Vol. 1, No. 2. Mobile Computing and Communications review is a publication of the ACM SIGMOBILE.
HomeRF based on Shared Wireless Access Protocol (SWAP), is another example of an operating environment which can be used to connect devices. A HomeRF Working Group was formed to provide the foundation for a broad range of interoperable consumer devices. The goal of the HomeRF Working group is to establish an open industry specification for wireless digital communication between PCs and consumer electronic devices anywhere in and around the home. The working group, which includes the leading companies from the personal computer, consumer electronics, peripherals, communications, software, and semiconductor industries, is developing a specification for wireless communications in the home called SWAP. The HomeRF SWAP system is designed to carry both voice and data traffic, and to operate in conjunction with the Public Switched Telephone Network (PSTN) and the Internet. The HomeRF SWAP system operates in the 2400 MHz band and uses a digital frequency hopping spread spectrum radio. The SWAP technology was derived from extensions of existing cordless telephone (DECT) and wireless LAN technology to enable a new class of home cordless services. It supports a time division multiple access (TDMA) service to provide delivery of interactive voice and other time-critical services. SWAP also supports a carrier sense multiple access/collision avoidance (CSMA/CA) service for delivery of high speed packet data. The SWAP system can operate either as an ad-hoc network or as a managed network under the control of a connection point. In an ad-hoc network, where only data communication is supported, all stations are equal and control of the network is distributed between stations. For time critical communications such as interactive voice, the connection point, which provides the gateway to the PSTN, is required to coordinate the system. Stations use the CSMA/CA to communicate with a connection point and other stations. The Swap specification 1.0 is incorporated by reference in its entirety.
The above-mentioned IEEE 802.11 standard for wireless LAN medium access control comprises features for conserving power. At regular intervals, with small random time offsets, LAN members broadcast information about themselves only. If a device receives such a broadcast while it is preparing one itself, it will not broadcast that round. In this way, all devices broadcast their individual characteristics with statistically even distribution. Because the medium access control (MAC) layer is given a specific addresses to which it directs transmissions, its image of the LAN does not need to be up-to-date. It is a clear disadvantage of the approach promulgated in IEEE 802.11 is that it may take some time until a newly arrived device or an absent device is announced/noticed. IEEE 802.11 LANs are centralized, star-shaped networks. It should also be noted that the 802.11 advertisements contain only communications characteristics and individual identify, not service offerings.
There are several more or less elaborate protocols and techniques that allow an ad-hoc wireless communication between mobile devices. The above described Bluetooth radio technology and HomeRF approach are prominent examples. All state-of-the-art protocols and techniques have certain drawbacks, as briefly addressed in the following section.
For seamless connection in an ad-hoc local network, the respective devices require a method for becoming aware (discovery) of the services offered by neighbors. In addition, the devices in such a network must make their own services known (advertisement). On one hand, the discovery and advertisement of services offered in a local network must be carried out in a timely manner, but on the other hand battery power must be conserved if portable devices are employed. A local network where entering the network is seamless such that the device can easily change locations is also desirable. It is desirable that no user intervention is required if a device enters or leaves an ad-hoc network. For example, it may be arduous if the user was required to pre-form a reconfiguration. It is also desirable that a device should be able to leave the network without formal notification.
It is an object of the present invention to provide a scheme for introducing a new device into an ad-hoc wireless local network. It is an object of the present invention to provide a scheme for a device in an ad-hoc wireless local network to announce its services to another device in the local network. It is an object of the present invention to provide a scheme for a device in an ad-hoc wireless local network to discover services provided by other devices in the local network.
The present invention concerns an apparatus for exchanging service information with other devices. The present apparatus comprises a transceiver, a processing unit, a memory for storing information about its local services and/or services provided by other devices, and a protocol resource manager.
This protocol resource manager performs the following steps. It triggers the transceiver to send service information, comprising information about itself and/or other known devices to other devices. It chooses a timeout value TA. The protocol resource manager ensures that the apparatus listens for up to a maximum time TA for service information received by the transceiver. If TA timed out without having received such service information by the transceiver, it triggers the transceiver to send service information, as stated above. If such service information was received by the transceiver prior to TA timing out, the protocol resource manager checks whether the service information received comprises information about itself. If it does, then it chooses another timeout value TA, and continues listening as stated above. If the protocol resource manager does not find that the information received contained information about itself, it triggers the transceiver to send the service information, as stated above.
The present invention also concerns a scheme for advertising service offerings in a communications system comprising two devices. The first device sends service information, comprising information about itself and/or other known devices. The first device chooses a timeout value TA, and listens for up to the maximum time TA for service information sent by another device. If TA timed out it sends the service information, as stated above. Otherwise, the first device checks whether the service information sent by another device comprises information about itself (local services). If the information does contain the information about itself it continues by choosing a timeout value TA, as stated above, otherwise the device sends the service information as stated above.
The present invention relates generally to local networks and more specifically, to a communication scheme which allows devices within the local network to announce their service and/or to discover services provided by other devices while limiting the power drain on battery powered devices. The present local networks typically have a hybrid mesh topology where a device may communicate with any other device. A peripheral device for instance may communicate with another peripheral device without a relay station or base station being involved.
The present solution combines advertisements and/or discovery with membership renewals. The general approach is that a group of devices will take turns broadcasting (advertising) a list of services (hereinafter referred to as service information) available. By using variable transmission delays that are reset when other advertisements are seen, and adjusting the distribution of these delays, new devices can quickly be identified, and absent machines can be noticed. The present invention provides a mechanism to form small private ad-hoc groupings of connected devices away from a fixed network infrastructure. With this invention, a solution is presented that, when used in combination with a wireless communication protocol, allows a network to be formed ad-hoc if needed, and dissolved if not needed anymore. According to the present invention a network of all eligible proximate devices (devices that will allow themselves to be networked) can be set up while allowing new devices to join and leave seamlessly.
All devices that form an ad-hoc grouping, according to the present invention, do not necessarily have identical implementations (from a software and/or hardware point of view) as long as at least the present service discovery protocol is implemented in all these devices.
One device may act as a master and the other(s) as slave(s). A device may be put into a power-saving mode in which the device activity is lowered. It is an advantage of the present scheme that battery power is conserved by using only a small number of transmissions.
The present scheme facilitates implementations where entering a local network is seamless in that it does not require user intervention. The present scheme also facilitates implementations where a device is able to leave a local network without formal notification.
Further advantages include: automatic adjustments to changes in the local area network; traffic volume is kept low; a device within a local network according to the present invention may change place in real time, a device may turn on or off arbitrarily, while the other devices within the vicinity monitor its appearance/disappearance on the network without posing an interference to any ongoing communication. Not all of the advantages above have to be realized in an implementation of the present scheme.